Voice telephony remains a major application of interest on mobile devices, such as smartphones. Typically, mobile devices implement voice telephony over circuits (similar to the public switch telephone network (PSTN)), once past the radio access network. In some cases, mobile devices may support a data channel, in addition to a voice channel (e.g., such devices may support concurrent voice and data communications). In such situations, a service provider may perform at least some voice call control functions over the data channel. However, even if a given device supports simultaneous voice and data communications, data communications may not be available on all networks, or may be sporadically unavailable, such that there may be situations where even though a voice call can be made, a data channel is unavailable.